European Journal of Cardiovascular Medicine

Macro creatine kinase (macro CK) type 1 is a rare, high-molecular-weight complex—most commonly a combination of CK-BB and immunoglobulin G (IgG)—that can significantly complicate the diagnosis of a myocardial infarction (MI) (1). Interaction with MI DiagnosisIn many modern laboratories, the presence of macro CK type 1 leads to false-positive results for MI when using traditional activity-based assays: False CK-MB Elevation: Standard “immunoinhibition” tests for CK-MB measure the B-subunit activity. Because macro CK type 1 contains the B-subunit but is not inhibited by the test reagents, it is erroneously measured as CK-MB.Activity Inversion: It often causes a “paradoxical” result where the measured CK-MB activity appears higher than the total CK level.(2) Persistent Elevation: Unlike the transient rise and fall of CK-MB during a true heart attack, macro CK levels remain persistently elevated over weeks or months. Macro CK type 1 itself is not a disease, it is frequently associated with underlying conditions that clinicians must differentiate from an acute cardiac event: Autoimmune Disorders: It is most strongly linked to autoimmune diseases, particularly myositis.Other Conditions: It has been observed in patients with cardiovascular disease, hypothyroidism, and certain malignancies

Case Presentation: Patient profile- 56-year-old male, known case of inflammatory bowel disease, likely Ileal Crohn’s Disease. He is non-smoker, non-alcoholic with no history of diabetes, angina, or angina-like symptoms. The patient underwent a routine annual health check-up where he was found to have an elevated CK-MB by the immunoinhibition assay. Despite being asymptomatic, a Treadmill Test (TMT) was conducted and turned out positive, though he remained symptom-free during the test. Further evaluation on Electrocardiogram (ECG) showed Sinus rhythm within normal limits. Echocardiography revealed normal Left Ventricle (LV) systolic function, Ejection Fraction (EF) 60%, no Regional Wall Motion Abnormality (RWMA). CT Coronary Angiography showed normal coronary arteries with zero coronary artery calcium (CAC) score, right dominant system.  Antinucler Antibody (ANA0 Profile, Liver Function Tests (LFT), and Kidney Function Tests (KFT) were all within normal limits. Other tests performed with results are depicted in Table 1.

Table 1:

Given the persistent elevation of CK-MB without clinical or imaging evidence of myocardial injury, the possibility of macroenzyme was considered. On 16 May 2025, CK electrophoresis demonstrated the presence of Macro CK Type 1, showing a band anodal to the CK-MM band (Figure 1). CK-MB by Mass Assay on the same day was 0.18 ng/ml (Normal <4.38 ng/ml).

Figure 1. Demonstrates the creatine kinase isoenzyme electrophoresis pattern obtained using the ISO CK/LD electrophoresis system. The gel strip shows the separation of CK isoenzymes based on their electrophoretic mobility. In this patient’s sample, an additional distinct band is observed migrating anodal to the CK-MM fraction, which is not part of the normal CK isoenzyme profile. This atypical band represents a macro-CK Type 1 fraction, a high–molecular-weight complex formed by the binding of CK (usually the CK-BB or CK-MM isoform) with immunoglobulin, most commonly IgG. The identification of this extra band through electrophoresis therefore establishes the diagnosis of Macro-CK Type 1, distinguishing it from true myocardial injury.

Creatine kinase is a cytosolic enzyme catalysing the reversible transfer of phosphate between creatine and adenosine diphosphate, maintaining ATP reserves in tissues with high energy demands such as skeletal and cardiac muscle, and brain (1). CK exists as three isoenzymes—CK-MM, CK-MB, and CK-BB—composed of M and B subunits (2). CK-MB is predominantly expressed in myocardial tissue, constituting up to 20% of total CK in the heart, whereas CK-MM predominates in skeletal muscle (3). Historically, CK-MB activity served as a cornerstone biomarker for the diagnosis of acute myocardial infarction (AMI), although it has largely been replaced by cardiac troponins due to their higher sensitivity and specificity (4). Nevertheless, CK-MB continues to be measured in some laboratories for cardiac injury assessment, particularly where troponin assays are unavailable. Macroenzymes are high-molecular-weight complexes of normal enzymes with immunoglobulins or other serum components, leading to decreased plasma clearance and artefactual enzyme elevations (5). Macro-CK refers to such complexes involving CK, and it is broadly classified into two types. Macro-CK 1 is an immunoglobulin-bound form—most commonly CK-BB or CK-MM complexed with IgG or IgA—whereas macro-CK 2 consists of oligomeric mitochondrial CK released into circulation (6-7). The reported prevalence of macro-CK 1 in the general population ranges between 0.5% and 3.7% (8). Though generally benign, macro-CK 1 may cause persistent or fluctuating CK elevations, leading to diagnostic confusion if unrecognised (9). The most clinically significant consequence of macro-CK 1 is assay interference. Conventional CK-MB activity assays use an immunoinhibition principle, where antibodies against the M subunit suppress CK-MM activity, and the remaining catalytic activity—assumed to originate from CK-MB—is measured(10). However, macro-CK 1, being resistant to inhibition, contributes spurious residual activity that falsely elevates CK-MB results (11). In extreme cases, apparent CK-MB values may exceed total CK activity, an analytical impossibility that immediately raises suspicion of macroenzyme interference (12) The present case displayed precisely this discrepancy: CK-MB activity exceeded total CK, yet CK-MB measured by mass assay was within normal limits, and cardiac troponin I remained negative. The combination of disproportionately high CK-MB activity with normal CK-MB mass and absent clinical evidence of myocardial injury provides a strong indication of assay interference by macro-CK 1(13-14). When confronted with discordant CK-MB results, the diagnostic approach should begin with repeat measurement using a different analytical principle—typically the CK-MB mass immunoassay or cardiac troponin testing (15). If the discrepancy persists, isoenzyme electrophoresis or gel filtration chromatography can confirm macro-CK by demonstrating an atypical electrophoretic band migrating anodal to CK-MM (16-17). In this patient, electrophoresis revealed a distinct macro-CK band confirming the diagnosis of macro-CK 1. Other biochemical red flags include persistently elevated CK-MB in asymptomatic patients, CK-MB/CK ratio > 1.0, and the absence of corresponding troponin elevation (18) Awareness of these indicators among clinicians and laboratory professionals can prevent extensive and unnecessary cardiovascular evaluation. Several studies have documented macro-CK 1 presenting as spurious CK-MB elevation. Davidson et al. reported five cases over a decade in which macro-CK 1 led to misleading CK-MB results, prompting unnecessary cardiac investigations(19). Horino et al. described macro-CK 1 associated with immune-mediated necrotising myopathy, further supporting its autoimmune link (20). Hsiao et al. analysed 16 patients with recurrent macro-CK 1, emphasising its benign, yet persistent nature and the importance of electrophoresis for confirmation (21). More recently, Cureus (2020) and BMC Cancer (2023) case series highlighted instances where CK-MB values exceeded total CK, underscoring that such discrepancies nearly always indicate analytical artefacts such as macroenzymes or CK-BB interference (22-23). This case reinforces the necessity of correlating laboratory findings with clinical context. Reliance solely on enzymatic activity assays without considering potential interferences may result in over-diagnosis of cardiac disease (24). Misinterpretation of elevated CK-MB can lead to unwarranted admissions, antiplatelet or anticoagulant therapy, and invasive procedures such as coronary angiography (25). The use of CK-MB mass assays and cardiac troponin should be prioritised whenever macroenzyme interference is suspected(26). Laboratory systems must incorporate flagging mechanisms for physiologically implausible results, such as CK-MB greater than total CK, and recommend confirmatory testing (27). Education of clinicians and technologists is equally vital to ensure appropriate test interpretation. Macro-CK 1 generally follows a benign course. Hsiao et al. observed persistence for months to years without clinical deterioration . Nevertheless, periodic monitoring of total CK and CK-MB mass is recommended to ensure stability and to detect any emerging true pathology. Patient counselling regarding the benign nature of the condition is essential to avoid anxiety and over-investigation (28). If macro-CK 2 or concurrent systemic illness is suspected, further evaluation including malignancy screening may be indicated (29). However, in this case, the electrophoretic pattern and clinical findings firmly support the diagnosis of macro-CK 1 with no malignant association.

In summary, this case demonstrates a classic example of macro-CK 1 causing persistently elevated CK-MB by immunoinhibition assay in a patient without cardiac disease. The discrepancy between CK-MB activity and mass, the absence of troponin elevation, and confirmation by electrophoresis firmly establish the diagnosis. Macro-CK 1 should be considered in any case of unexplained or discordant CK-MB elevation. Early recognition allows clinicians to avoid inappropriate treatment and invasive cardiac evaluation. Laboratories must implement robust interpretive algorithms and clinician education to identify such interferences promptly.

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